The present invention relates generally to mechanical fasteners and more particularly to captive spring-loaded fastener retainers.
Fastening devices are used in a variety of industrial and electronic applications to assist users in equipment assembly. For example, electrical units (e.g., meter cabinets, bus bar terminal boxes, modular panelboards, etc.) must be fastened together and/or must be secured to a wall or other object. During an installation process, these electrical units are attached to each other with bolts, nuts, and/or other fasteners.
Conventionally, a fastener is fixed into the side (e.g., caused to protrude through a hole, etc.) of one unit before the unit is abutted with another unit. Alternatively, a loose fastener (e.g., an unrestrained bolt, etc) is inserted into a hole in one unit by a user during the installation process. These are user unfriendly processes as it is difficult to align and/or maintain the alignment of multiple units before they are joined. If the units are not well-aligned, the fastener may break or damage one or both units during installation. Additionally, the loose fastener could be pushed out of the unit during the installation process and be lost or delay the installation process.
To avoid these complications, retractable captive fasteners, such as those described in U.S. Pat. Nos. 3,986,544 and 4,031,395, are used. With captive fastening devices, the possibility of dropping a fastener and losing it in the interior of the unit is diminished. Existing fastening devices of this kind restrain one of the members (e.g., a bolt, etc.) by holding it captive in a structural unit, but the other member (e., a nut, etc.) of a two-part fastener is left free.
In some cases, the fastening device has both pieces of a two-part fastener captivated. One part (e.g., the bolt) is captively mounted by notching or slotting a portion (e.g., the bolt head) so that it may be slidably mounted on “rails.” In this way, the bolt may move reciprocally in an axial direction but not rotationally relative to the assembly in which it is held. The other part (e.g. the nut) of the two-part fastener is mounted in such a way that it may move rotationally but not reciprocally with respect to the assembly in which it is held.
While these retractable captive fasteners provide improvements over the fixed or loose bolt design, they are still deficient. The retractable fastener may still be pushed back into the captivator during installation. This presents similar problems non-captive fasteners in that it may be difficult for a user to locate and/or access the retracted fastener. Additionally these captive fasteners require a single unit design and “off-the-shelf” fasteners cannot be used since they do not have appropriately slotted or notched heads. As such, these systems are relatively expensive and do not have any simple substitute fastener should the original fastener become fouled (e.g., bent, stripped, etc.) or lost during transit or installation.
Accordingly, flexible and cost-effective systems for fastening are required.